"When I got back I told my tutor at university and he asked me whether it was an interview," he said. "If it was, it seems I didn't get the job." Baddum-tish!

It's hard to fathom how a jape about being recruited by the KGB was supposed to help thaw glacial relations – Vladimir Putin hasn't spoken to a British leader in six years – that fell apart over a dissident's allegedly state-sponsored murder. But it wouldn't be the first time Cameron got himself in trouble with a doomed attempt at being lighthearted.

It was only two weeks ago that the PM managed the near impossible – eliciting widespread sympathy for Nadine Dorries – when he answered her question with the words "I know the honourable lady is extremely frustrated ..." before dissolving into laughter as if the humour unleashed by this remark were completely overpowering. The incident, for which he later felt obliged to apologise, came after his famously witty "Calm down, dear" riposte to Angela Eagle, and a peculiar set-piece answer to a question about the Greek bailout put by the MP Peter Bone (wait for it) on behalf of his wife. "I do feel now that a very big part of my life is trying to give pleasure to Mrs Bone," said Cameron, "but I feel on this occasion I can only go so far."

The problem with Cameron's terrible Commons jokes is how well they're received. In that chamber – a veritable golf club changing room of male bravado – sexism is inherently funny, and the unintentional double-entendre is the highest form of wit. On these occasions Cameron has actually read his audience perfectly. It's only later, on the news and on YouTube, that the joke falls flat.

Cameron's by no means the least funny Tory in the world, or even on the front bench. George Osborne's witless, toffee-nosed vulgarity – he is the master of what one might term the unpleasantry – manages to draw disapproving gasps even in the House. Take his riposte to gay MP Chris Bryant, who last Christmas asked the chancellor to be a bit less like Baron Hardup with regard to spending cuts, and a bit more like Prince Charming.

"Well at least I'm not the pantomime dame," said Osborne. Just last week, while gracelessly accepting the GQ Politician of the Year award he said: "I'm not sure who actually reads the political pages of GQ magazine. I suspect they're the only pages the teenage boy hasn't stuck together in reading the magazine." As awards presenter David Mitchell said, "I think that's lowered the tone."